There are many industrial operations which produce large quantities of material that must be collected in a tank and then removed from the tank for further processing or disposition. Such material may vary in size from rather small particles of a sand-like character up to material the size of crushed stone with occasional pieces weighing several hundred pounds. Often such tanks constitute water filled quenching tanks to receive the bottom ash that is produced in huge quantities in various types of solid material burning furnaces. Such tanks are commonly of an elongated rectangular shape, and in the case of a quenching tank the bottom of the furnace commonly has a water seal which is spaced inwardly from the tank walls and extends below the waterline.
In other cases the tank may be a dewatering tank into which material laden water is loaded for dewatering.
There has, for many years, been a need for a rugged and dependable drag bucket type of apparatus which can be used to remove material from such a tank, either periodically as required or continuously in repetitive cycles. Typical of equipment with which such apparatus may be used are the high capacity coal burning furnaces used in large electric power generating plants. Such a furnace may require a quenching tank in excess of 60 feet long and capable of handling an ash output of several tons an hour. The material delivered through the furnace grates varies in size from that of coarse gravel to several hundred pound chunks. For such an application the drag bucket apparatus must be capable of cycling for extended periods of time without the intervention of any human attendant, and must be adaptable to the varying conditions created by such a wide range of material sizes.
Another typical application for such apparatus is to receive the output of a bank burner which is used to consume and dispose of the enormous quantities of unusable bark produced in a lumbering operation. A bark burner may require a quenching tank no more than about 15 feet in length.